The present invention relates to a hydraulic cylinder with end position damping including at least one cylinder in which at least one piston is arranged that is connected to at least one piston rod and is displaceable in axial direction, wherein the piston divides the cylinder into a piston side and a piston-rod side and the hydraulic oil, required for actuation of the piston, is pumped from a hydraulic pump via inlet and outlet lines through inlet and outlet bores provided on the cylinder. The invention also relates to a shovel excavator having the hydraulic cylinder according to the invention.
End position damping is required for numerous machines and devices, wherein masses in motion have to be decelerated within defined standards. Thus end position damping ensures a soft deceleration of the hydraulic cylinder's speed at both of its end positions or also only at one end position in order to prevent damage to the piston or the respective end position of the chamber due to a high velocity impact of the piston. This is required because the systems for agricultural and construction machines not only have to meet high standards concerning durability during operation, but also increased functionality and in some cases health-relevant demands for comfort are considered imopeningant. High performance machines therefore require means that are able to absorb impacts and vibrations so as to efficiently protect humans and machines from overload. This is also intended to reduce noise pollution of the environment.
For this purpose dampers are known from the state of the art that operate based on a throttling of the fluid flow. Thereby, the kinetic energy resulting from the movement is converted into heat. The kinetic energy E as the product of all masses m acting on the piston rod and the stroke speed v at the beginning of the damping should not exceed the working volume W of the damping. It is generally known that this may be realized at the end positions by means of additions to the hydraulic cylinder having damping pistons with a smaller cross-section.
For instance, a piston or a tappet seals an outlet opening that is provided for drainage of hydraulic oil, as soon as the piston in the hydraulic cylinder is fully retracted or extended. Thereby, the hydraulic oil is forced to flow out of the cylinder chamber through a bypass that has a smaller cross-section than the outlet opening. The cross-section of the bypass is usually adjustable through a grub screw. Hereby, the cylinder is significantly slowed down and damped until reaching its end position.
These end position damping systems have proven their worth; however, they have the disadvantage that end position damping is achieved through additional components in and on the hydraulic cylinder. Furthermore, the adjustability and the calibration of the end position damping through grub screws or comparable means does not function entirely without difficulties due to the fact that an over- or underdamping may cause damage to the hydraulic cylinder. Additionally, electrical measuring technology is used in order to prevent the piston to impact the mechanical stops at full speed. The overall system may suffer considerable damage in the case of failure of the components that have been additionally included in the cylinder.